Spark-plug.



W. S. THOMAS.

SPARK PLUG.

APPLICATION FILED FEB. 23, 19|s.

1,300,048. Patented Apr. 8, 1919.

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UNITED STATES PATENT OFFICE. l

WILLIAM S. THOMAS, OF LOCK HAVEN, PENNSYLVANIA, ASSIGNOR T0 THOMAS SPARK PLUG- COMPANY, OF NEW YORK, N. Y.

SPARK-PLUG.

Application filed February 23, 1918.

To all whom z'z may concern.'

Be it known that I, VILLIAM S. THOMAS, a citizen of the United States, residing at Lock Haven, in the county of Clin-ton and State of Pennsylvania, have invented certain new and useful Improvements in Spark-Plugs, of which the following is a specification.

One object of my imention is lto so construct cert-ain of the parts of a spark plug that an exceptionally large or fat spark will be produced between the electrodes thereby effecting proper ignition and at the same time keeping the electrodes clean at their sparking portions. n

Another object is to so construct my 1mproved spark plug as to reduce, to a minimum, current leakage through the several parts.

A still further object is to so construct the insulated electrode of my improved spark plug that it can be easily removed from its insulator and when in service can be secured in firm engagement with its insulator to prevent current leakage, as above mentioned, and also to protect it and the interior of the electrode insulator from the products of combustion.

These objects, and other advantageous ends which will be described hereinafter, I attain in the following manner, reference being had to the accompanying drawing in which- The figure of drawing is a central sectional elevation through a spark plug including my present invention.

Referring to the drawing, l represents a metallic casing which has a ground electrode 2 thereon. This casing 1 has a stem 3 which is externally screw threaded, as shown at 4, so that the casing can be screwed within an engine cylinder or the like. The casing 1 has =a bore 5 which is of a. larger diameter than a Ibore 6 in the stem 3. The bore 5 terminates at its bottom in a shoulder 7, and a tapered or frusto-conical passage 8 extends downwardly from the shoulder 7 to the passage 6. Thus the bore 5, frusto-conical passage 8, and passage 6 are all in communication with each other. The casing 1 at its top is provided with a cavity 9 which communicates with the bore 5 and is of larger diameter than the bore 5, thus providing a ledge 10.

The extreme upper portion of the cavity Specification of Letters Patent.

Patented Apr. 8, 1919.

serial No. 218,702.

9 is internally screw threaded at 11 t0 receive an externally screw threaded sleeve 12 of a nut` 13, the opening 1l of the sleeve also extending' through the nut 13.

An elongated insulated electrode 15 extends through a passagel 16 in an electrode insulator or covering 17 which is preferably made of porcelain. The insulator 17 has an annular enlargement 18 within its length. The annular enlargement 18 is preferably made with substantially fiat upper and lower surfaces 19 and 20, respectively, which provide substantially parallel shoulders for a purpose hereinafter described.

An auxiliary insulating band of mica or other insulating material 21 is positioned around the annular enlargement 18 and this band is preferably made in two telescoping sections 22 and 23. The .bottom section 23 has an inturned flange 2a which is adapted to engage the shoulder 20 and to surround the lower stem portion 25 of the insulator 17. The upper portion of the section 22 has an internal flange 26 which surrounds the upper stem portion 27 of the insulator 17 andengages the shoulder 19 of the annular enlargement 18 of the electrode 17. Thus the enlargement 18 of the electrode 17 is housed within the mica band 21. The band 21 is preferably made by cutting a block of mica on a lathe or other machine and afterward the band is tightly fitted around the enlargement 18 of the insulator 17.

The band 21 is inclosed within a metallic jacket 28. This jacket includes upper and lower anges 29 and 30, respectively, which are preferably pressed inwardly by a pressure device (not illustrated). A washer 31, which is preferably made U-shape in cross section, is interposed between the inner edge surface of the flange 26 and the stem 27 a portion of this washer also being interposed between the flange 29 of the jacket 28 and the annular enlargement 18 of the electrode 17 Another washer 32, preferably of the same general formation as the washer 31, is interposed between the inner edge surface of the band flange 2st and the electrode stem 25. This washer 32 is also located between the jacket flange 30 and the surface 20 of the electrode enlargement 18. The jacket 28 is of such height and external diameter that it lits within the bore 5 of the casing 1 and rests on the shoulder 7, the upper surface of the jacket being on the level with the ledge 10.

' A washer 33 rests jointly on the ledge 1() and the upper surface of the jacket 28 so as to bridge the parting between the casing and the jacket. The lower end of the sleeve 12 has a portion directly above the parting between the jacket 28 and the casing 1 and this portion of the sleeve is designed to engage the top of the washer 33 thereby rigidly holding the jacket 28 against the shoulder 7 of the casing 1, said washer also serving as a seal to prevent any possible leakage between the jacket and the casing.

-It will be further noted that by this arrangement the pressure of the sleeve v12 is imparted to the jacket 28 at a position beyond and outside of the outer diameter of the annular enlargement 18 of the electrode 17 so that with the arrangement as illusl trated there will be practically no pressure by thesleeve 12 and nut 13 on the annular enlargement 18 of the electrode 17 Thus no matter how much the nut is tightened itis practically impossible to fracture the electrode enlargement 18. s

The electrode 15 is made of varying diameter throughout its length; for example as illustrated in the. drawing, the portions 34, 35, and 36 are of comparatively small diameter, while the intervening portions 37 and 38 are of comparatively large diameter. The reason for making the electrode alternately of Vlarge and small diameter is to step the current rapidly up and down during its passage therethrough.

The electrode 15 adj acentits lower end is provided with a frusto-conical enlargement. 39;- Thisenlargement 39 tapers upwardly and is adapted toY engage a frusto-conical seat 40 in the bottom of the electrode insulator 17 The portion 41 of the electrode 15 which depends downwardly from the frusto-conical portion 39 is of small diameter1 compared to the frusto-conical enlargement 39 and the portions 37 and 38 above described. This portion 41 of the electrode 15 is the sparking portion of the electrode and has its lower end located adjacent the ground electrode 2v so that the spark is formed in the space between these two electrodes. i

The upperV portion of the electrode 15 is screw threaded andpasses centrally through a cap 42 on the top of the electrode insulator 17. Av nut A43"fits the upper screw threaded end of the electrode 15 and engages the top of thecap 42. Thus by turning the nut 43 the electrode Y15 will move longitudinally with respect to the insulator 17 so as to tightly jam the frusto-conical enlargement 39 against and within the seat 40 at the bottom'of the electrode'insulator 17.

.The passage 16 is preferably made of Y larger 1 diameter than Athe diameters of the portions 37 and 38 so that there is a clearance space between these latter mentioned portions and the electrode insulator 17. By this construction I reduce to a minimum the possibility of current leakage between the electrode 15 and the insulator 17 The upper threaded end of the electrode insulator 17 is provided with a binding nut 44 and between this nut 44 and the nut 43 insulator 17 In other words the top sur-Y face of the jacket 28 is in a plane intersecting the electrode 15 below the enlarged portion 37, and the lower surface of the jacket 28 is in a plane intersecting the electrode 15 above the enlargement 38. By this arrangement a comparatively large free space is provided between the-electrode and its insulator within thezone of the jacket 28 so that current leakage at this point is practically impossible.

In my United States Patent No. 1,255,826, February 5, 1918, I have described and claimed the construction and arrangement of the jacket, casing, and sleeve, as above described and I do not claim these features per se 1n the present application. Furthermore, the mica band in combination with a jacket forms a part of my co-pending appli- Y cation for United States patentkled J anuary 4, 1918, Serial No. 210,252, and I there: fore do not claim'these latter mentioned elements per se in the present application. However, there is a co-action between the particular form of insulated electrode and the jacket, band, and annular enlargement, as above described and in so-far as this combination exists Imake claim in this application to this combination of parts inaddition to the construction andY arrangement of the electrode 15 and electrode insulator 17 l/Vhile I have described my invention as taking a particular form, it will be understood that the various parts of my invention may be changed without departing from the spirit thereof, and hence Ido not limit myself to the precise construction set forth, but consider that I am at liberty to make such changes and alterations as fairly come within the scope of thev appended claims.- Y

Having thus described my invention,-what I claim as new and desire to secure by Letters Patent is: j j l' VV 1. yThe combination of anelectrodeinsulator having a passage extending therethrough; and an electrode positioned within said passage and including portions of relatively small and large cross section positioned alternately within its length, said passage being wider than the width of said relatively large and small portions of the electrode so as to provide a clearance between themv and the insulator, substantially as described.

2. The combination of an electrode insulator having a passage extending therethrough an electrode positioned within said passage and including portions of relatively small and large cross section positioned alternately within its length; and a jacket surrounding said insulator, said jacket being located in a zone defined by parallel planes intersecting said electrode between two of said relatively large portions t-hereof, substantially as described.

3. The combination of an electrode insulator having a passage extending therethrough; an electrode positioned within said passage and including portions of relatively small and large cross section positioned alternately within its length; a jacket surrounding said insulator, said 'jacket being located in a zone dened by parallel planes intersecting said electrode between tWo vof said relatively large portions thereof; and a mica band interposed between said jacket and the electrode insulator, substantially as described.

4. The combination of an electrode sulator having a passage extending therethrough; an electrode positioned within said passage and including portions of relatively small and large cross section positioned alternately within its length; a metallic jacket surrounding said insulator, said jacket being located in a Zone defined by parallel planes intersecting said electrode between two of said relatively large portions thereof; an insulating band interposed between said acket and the electrode insulator, said electrode insulator having an enlarged portion in engagement with said band; and washers interposed between iianges of said jacket and band and the electrode insulator, substanv tially as described. Y. In testimony whereof I have signed my name to this speciiication in the presence of two subscribing witnesses.

VILLIAM S. THOMAS. Vitnesses MARY A. INGLAR, CHAs. E. Po'rrs.

Copies of thispatent may be obtained for ve cents each, by addressing the Commissioner of Patents, Washington, D. C. 

